Impedance switching timer

ABSTRACT

The timing circuit is connected in series relation with the coil of a contactor and the same includes a charging circuit and a conducting circuit. A resistor of high ohmic value and a series connected condenser form the charging circuit. Since the resistor is relatively high in ohms the charging of the condenser is delayed to give the desired time delay interval to the timing circuit. The conducting circuit includes a magnetically actuated reed switch and an inductance coil which is wound around the glass enclosed reed switch. A trigger diode which is caused to close when the condenser is charged to a predetermined voltage effects a discharge of the condenser through the inductance coil.

United States Patent 3,267,302 8/1966 Breiner et al. 317/141 X 3,312,0814/1967 Berger et al. 317/22 X 3,422,379 1/1969 Rowell 317/141 X3,434,028 3/1969 McCready 317/36 X Primary Examiner-Otis L. RaderAssistant Examiner- Robert J. Hickey Attorney-Russell 1-1. ClarkABSTRACT: The timing circuit is connected in series relation with thecoil of a contactor and the same includes a charging circuit and aconducting circuit. A resistor of high ohmic value and a seriesconnected condenser form the charging circuit. Since the resistor isrelatively high in ohms the charging of the condenser is delayed to givethe desired time delay interval to the timing circuit. The conductingcircuit includes a magnetically actuated reed switch and an inductancecoil which is wound around the glass enclosed reed switch. A triggerdiode which is caused to close when the condenser is charged to apredetermined voltage effects a discharge of the condenser through theinductance coil.

[72] Inventors Ernie Foldvari Cerpentersville; Dennis C. Walstad,Winfield, both oi I11. [2]] Appl. No. 858,993 [22] Filed Sept. 18, 1969[45] Patented Nov. 2, 1971 [73] Assignee Fumes Electric Company Bntevia,Ill.

[54] IMPEDANCE SWITCHING TIMER 3 Chill, 2 Drawing Figs.

[52] US. Cl 317/142, 307/132, 307/293, 318/484, 317/36 [51] Int.Cl...II0lh47/l8 [50] Field of Search 318/484,

[56] References Cited UNITED STATES PATENTS 3,182,227 5/1965 Brittain etal 307/132 X 3,119,951 1/1964 Davy 3l7/36X Z6 20 J6 J7 PATENTEDNUV 21911 and, G

Dem

IMPEDANCE SWITCHING TIMER The invention relates to electronic timingcircuits for controlling the operation of electric motors and the likeand has reference more particularly to an electronic circuit which willpresent a relatively high impedance preventing current flow for apredetermined time interval and wherein the impedance is reduced to arelatively low value to start current flow and thereafter to maintaincurrent flow.

The timing circuit of the invention is connected in series with certaincontrol switches such as a thermostat, a safety switch and/or a pressureswitch and also in series with the coil of the motor contactor. Thecircuit arrangement is then connected across the terminals of the powersupply and in shunt relation with the electric motor or other device tobe controlled. When the control switches such as the thermostat, thesafety switch and pressure switch are closed, the voltage of the powersupply is applied to the timing circuit. However the timing circuit withact as an open switch until a predetermined time interval has elapsed atthe end of which current flow takes place to energize the coil of thecontactor and with the closing of the contactor the motor or otherdevice is also energized.

An object of the invention resides in the provision of a timing circuitwhich will have a sufficiently high impedance to form an open circuitpreventing current flow when its terminals are connected across a powersupply, but wherein the impedance of the circuit will be reducedmaterially to start current flow and thereafter to maintain currentflow.

A more specific object of the invention is to provide an electronictiming circuit wherein a selected value of capacitance in series with aselected value of resistance to control the charging rate of thecapacitance will give the desired time interval during which theoperation of the motor is delayed following the closing of all thecontrol switches.

Another object is to provide an electric circuit having a built-intiming delay feature and which will also incorporate a capacitor forsmoothing the full-wave rectified current and for maintaining minimumcurrent flow when the voltage attains a minimum value at the end of eachhalf wave pulse of the rectified current.

Another object of the invention resides in the provision of anelectronic timing circuit which can be preset as regards the time delayinterval by selecting certain values of resistance and capacitance andwhich will also have a fast drop out since the circuit will openimmediately in the event of any chattering of the thermostat or othercontrol switch or any momentary interruption in the power supply.

With these and various other objects in view, the invention may consistof certain novel features of construction and operation, as will be morefully described and particularly pointed out in the specification,drawings and claims appended thereto.

In the drawings which illustrate an embodiment of the device and whereinlike reference characters are used to designate like parts:

FIG. I is a diagrammatic view of a control circuit arrangement for anelectric motor and which incorporates the timing circuit of theinvention; and

FIG. 2 is a diagrammatic view of the timing circuit showing the same inseries with several control switches and in series with the coil of themotor contactor.

The diagrammatic circuit arrangement shown in FIG. 1 illustrates animportant and extensive use of the present timing circuit, namely asprotection for an electric motor such as 10. The motor may be acompressor motor such as may be used in air conditioning equipment andthe conductors 11 and 12 electrically connect the motor to the leads L,and L, of a source of alternating current. Switching means in the formof a motor contactor I4 is interposed in the conductors l1 and 12 andthe coil of said contactor indicated by the numeral 15 is connectedacross the power source in shunt relation with the motor 10.

The numeral 16 indicates the timing circuit in its entirety and saidtiming circuit is in series relation with the coil 15. The

circuit and said coil are also connected in series with certain controlswitches such as the thermostatic switch 17, the safety switch 18 andthe pressure switch 20. In the event the incoming power supply ismomentarily interrupted due to lightning or other reasons for more than15 or 20 milliseconds, the timing circuit will open to deenergize thecontactor coil, and current flow to the compressor motor is thusterminated. After a preset time delay on the order of several minutesthe timing device will restore current flow provided the controlswitches remain closed. Similar operation takes place in the event ofthermostat chatter such as may interrupt current flow to the timingcircuit for more than 15 or 20 milliseconds. The reset time afterdeenergization under any condition is a matter of minutes depending onthe values of the components employed in timing circuit. The device willthen automatically reset and complete the control circuit to againenergize the coil 15 of the contactor 14. This reset time protects themotor from short cycling since reset does not occur before a lapse of 2or 3 minutes.

Referring to FIG. 2 which illustrates in diagrammatic form the detailsof the timing circuit, it will be seen that the conductors 22 and 23connect at the terminals 24 and 25 with the respective sides of a diodebridge for full wave rectification of the alternating current obtainedfrom I... L,. Terminal 24 has connection withthe rectifiers 26 and 27whereas terminal 25 connects with the rectifiers 28 and 30. Theconductor 31 is thus the positive side of the bridge with the conductor32 forming the negative side. The resistance 33 and the capacitor 34 areconnected in series across the conductors 31 and 32. The resistance 33is relatively high in value on the order of 1.5 megohms although itsresistance in ohms will vary depending on the time delay desired. Thecapacitor 34 designed for about 75 volts will have a value ofapproximately 200 microfarads. However, here again the selection willdepend on the time delay interval desired for the circuit. The reedswitch 35 and the coil 36 are also connected in series with each otherand across the conductors 31 and 32. The coil 36 is physically woundaround the glass enclosed reed switch so that the magnetic flux causedby current flow through the coil will cause the contacts of the reedswitch to close.

The resistance 37 and the trigger diode or diac 38 are joined in seriesand the same are connected at one end 40 between the resistance 33 andthe capacitor 34 and at the opposite end the same are connected at 41between reed switch 35 and the coil 36. The diode 42 is connected at 43between the resistance 37 and the diac 38 and at its opposite end thediode is joined to the conductor 31. Another connection leading from 41includes the capacitor 44 which is connected at 45 with the negativeconductor 32. The value of resistor 37 is relatively low on the order ofohms. The diac 38 is a switching device sensitive to voltage, and whenapproximately 60 volts, as regards the circuit of FIG. 2, areappliedthereto the diac is caused to close. The capacitor 44 is designed forabout 20-volt operation and has a value of approximately 60 microfarads.

It is believed that operation of the timing circuit will be clear andfully understood from the description of the various components.However, it can be stated that current flow taking place throughresistance 33 will charge the condenser 34. However, the charging timeis slow due to the high value in ohms of the resistor 33 which gives thetime delay in minutes such as may be desired. The condenser 34 willdischarge through the resistance 37 when the voltage across the diacreaches approximately 60 volts, the diac having been selected for suchclosing at the stated voltage. The discharge current will thus flowthrough the coil 36 and the resulting flux will cause the reed switch toclose. With the closing of the reed switch the impedance of the timingcircuit is materially reduced since the current now bypass the high ohmresistor 33 and flows through the reed switch and the coil which have arelatively low impedance. The condenser 44 is connected across the coil36 in order to smooth out the pulses of the fullwave rectified currentand maintain current flow through the coil even when the half-wavepulses attain a minimum or zero voltage. It is necessary to maintaincurrent flow through the coil 36 or else the reed switch wouldinadvertently open. The diode d2 is provided so as to allow thecapacitor 34 to fully discharge. Otherwise the next operation mightpossibly take place with 34 partly charged which would shorten the timedelay interval.

In the event the control switches l7, l8 and should open or in the eventthe supply current should be interrupted, then the current flow in thecoil will cease and the reed switch will immediately open. Accordinglyit will be understood that the present timing circuit has a fastdropout. Also, even though voltage is immediately applied to theterminals 24 and 25 of the timing circuit, the coil iii of the contactorwill not be energized until the time delay period for the timer haselapsed. In other words, the timing circuit does not reset itselffollowing deenergization of the contactor coil until the delay timeinterval for the circuit has elapsed. This reset time helps to protectthe motor from short cycling by preventing the motor from starting upuntil a delay of 2 or 3 minutes after the motor has stopped for anyreason. This is particularly advantageous for hermetic compressor motorswhich are often unable to restart until the head pressure of refrigerantgas has been dissipated through the expansion valve.

The timing circuit is connected across the motor terminals in advance ofthe contactor and upon closing of the control switches the rectifiedvoltage is immediately applied to cause charging of the condenser 34 atthe rate determined by the resistance value of 33. This charging circuitas the same may be termed is in parallel with the conducting circuitincluding the reed switch 35 and the inductance coil 36. The tripcircuit consists of the trigger diode or diac 38 which is sensitive tovoltage. Accordingly when the condenser 34 has been charged to a valueas determined by the diac, the same is caused to close and the condenser34 discharges through the coil 36.

What is claimed is:

1. In a timing circuit of the character described, the combination witha source of alternating current, of a diode bridge circuit for full-waverectification having its terminals connected across the current source,a charging circuit consisting of a high ohmic value resistor in seriesrelation with a first condenser, the resistor being connected to thepositive terminal of the bridge and the condenser being connected to thenegative terminal of the bridge. A parallel conducting circuitconsisting of a magnetically actuated reed switch in series connectedrelation with an inductance coil, the reed switch being connected tosaid positive terminal and the coil being connected to the negativeterminal of the bridge circuit, said coil having inductive relation withthe reed switch whereby the reed switch is caused to close when currentflows through the coil, a trip circuit including a trigger diode whichis caused to close when a preselected voltage is applied to itsterminals, a conductor connecting the trigger diode to the chargingcircuit between the resistor and the first condenser and to theconducting circuit between the reed switch and the inductance coil,whereby when the first condenser is charged to the preselected voltagethe diode closes to discharge the first condenser through the inductancecoil, a second condenser connected across the inductance coil forsmoothing out the current flow as rectified by the bridge and a diodehaving one side thereof electrically connected to said conductor at alocation between the trigger diode and its connection to the chargingcircuit and having its other side connected to the positive terminal ofthe bridge circuit, whereby the first condenser may fully dischargebefore another charging of said condenser begins to take place.

2. In a timing circuit having terminals connected across a source ofelectric current, in combination, a first resistor and a firstcondenser, said first resistor having electrical connection to oneterminal and having a series connected relation with the first condenserwhich is connected to the other terminal, said resistor having arelatively high resistance value so as to cause the condenser to chargeat a relatively slow preselected rate, first switch means of thesensitive-to-voltage type and having such connection with the firstresistor-first condenser series circuit that the first condenser upondischarge will cause current to flow through the said first switchmeans, an inductance coil and second switch means in series connectedrelation, the inductance coil having electrical connection to oneterminal and the second switch means being connected to the otherterminal of the timing circuit, said second switch means being glassenclosed and of the magnetically actuated type and the inductance coilhaving an inductive relation therewith, said coil and second switchmeans having such electrical connection with the first switch means ofthe sensitiveto-voltage type that upon current flow taking place throughthe same the said current is caused to also flow through the in ductancecoil, whereby the second switch means is caused to close due to themagnetic action of the inductance coil on the second switch means whencurrent flows through the inductance coil, said second switch means whenclosed together with the inductance coil providing a path for currentflow of considerably less impedance than the path provided by the firstresistor of high ohmic value and its series connected first condenser, asecond condenser connected across the inductance coil for maintainingcurrent flow through the coil for as long as the second switch meansremains closed, and a diode having one side thereof electricallyconnected in circuit between said first switch means of thesensitive-to-voltage type and the connection thereof to the firstresistor-first condenser series circuit and having its other sideconnected to the positive terminal of the timing circuit, whereby thefirst con denser may fully discharge before another charging of saidcondenser starts to take place.

3. A timing circuit having terminals connected across a source ofelectric current as defined by claim 2, wherein the first switch meansof the sensitive-to-voltage type consists of a diac which provides anormally open switch, wherein its connection in the timing circuit issuch that the diac is caused to close when the first condenser has beencharged to a preselected value, and wherein with the closing of the diacthe first condenser discharges through the same.

1. In a timing circuit of the character described, the combination witha source of alternating current, of a diode bridge circuit for full-waverectification having its terminals connected across the current source,a charging circuit consisting of a high ohmic value resistor in seriesrelation with a first condenser, the resistor being connected to thepositive terminal of the bridge and the condenser being connected to thenegative terminal of the bridge. A parallel conducting circuitconsisting of a magnetically actuated reed switch in series connectedrelation with an inductance coil, the reed switch being connected tosaid positive terminal and the coil being connected to the negativeterminal of the bridge circuit, said coil having inductive relation withthe reed switch whereby the reed switch is caused to close when currentflows through the coil, a trip circuit including a trigger diode whichis caused to close when a preselected voltage is applied to itsterminals, a conductor connecting the trigger diode to the chargingcircuit between the resistor and the first condenser and to theconducting circuit between the reed switch and the inductance coil,whereby when the first condenser is charged to the preselected voltagethe diode closes to discharge the first condenser through the inductancecoil, a second condenser connected across the inductance coil forsmoothing out the current flow as rectified by the bridge and a diodehaving one side thereof electrically connected to said conductor at alocation between the trigger diode and its connection to the chargingcircuit and having its other side connected to the positive terminal ofthe bridge circuit, whereby the first condenser may fully dischargebefore another charging of said condenser begins to take place.
 2. In atiming circuit having terminals connected across a source of electriccurrent, in combination, a first resistor and a first condenser, saidfirst resistor having electrical connection to one terminal and having aseries connected relation with the first condenser which is connected tothe other terminal, said resistor having a relatively high resistancevalue so as to cause the condenser to charge at a relatively slowpreselected rate, first switch means of the sensitive-to-voltage typeand having such connection with the first resistor-first condenserseries circuit that the first condenser upon discharge will causecurrent to flow through the said first switch means, an inductance coiland second switch means in series connected relation, the inductancecoil having electrical connection to one terminal and the second switchmeans being connected to the other terminal of the timing circuit, saidsecond switch means being glass enclosed and of the magneticallyactuated type and the inductance coil having an inductive relationtherewith, said coil and second switch means having such electricalconnection with the first switch means of the sensitive-to-voltage typethat upon current flow taking place through the same the said current iscaused to also flow through the inductance coil, whereby the secondswitch means is caused to close due to the magnetic action of theinductance coil on the second switch means when current flows throughthe inductance coil, said second switch means when closed together withthe inductance coil providing a path for current flow of considerablyless impedance than the path provided by the first resistor of highohmic value and its series connected first condenser, a second condenserconnected across the inductance coil for maintaining current flowthrough the coil for as long as the second switch means remains closed,and a diode having one side thereof electrically connected in circuitbetween said first switch means of the sensitive-to-voltage type and theconnection thereof to the first resistor-first condenser series circuitand having its other sIde connected to the positive terminal of thetiming circuit, whereby the first condenser may fully discharge beforeanother charging of said condenser starts to take place.
 3. A timingcircuit having terminals connected across a source of electric currentas defined by claim 2, wherein the first switch means of thesensitive-to-voltage type consists of a diac which provides a normallyopen switch, wherein its connection in the timing circuit is such thatthe diac is caused to close when the first condenser has been charged toa preselected value, and wherein with the closing of the diac the firstcondenser discharges through the same.